Roof bit body and insert assembly

ABSTRACT

A center vacuum rotary drill bit including a rotary drill bit body and an insert. The bottom surface of the slot has a projecting key that cooperates with a depression keyway of the insert. Generally vertical sidewall surfaces of a depression keyway and vertical surfaces of a projection key provide mechanical resistance against lateral movement of the cutting insert. This mechanical resistance reduces displacement of the insert with respect to the bit body during brazing and thus a high quality, accurately aligned drill bit assembly is provided by applicants&#39; invention. The depression keyway is designed so as to minimize the effect of the axial load on the insert by avoiding sharp corners which tend to amplify nominal stress and provides an insert of a proper carbide density after pressing. Integral bit body protuberance means adequately separate the insert within the slot and permit braze flow between the insert and slot. The protuberance means enhance braze flow when braze is fed between the insert body and bit body.

RELATED APPLICATIONS

[0001] This application is related to copending U.S. patent applicationSer. No. 09/376,725, filed Aug. 17, 1999, to Ted R. Massa et al. (CaseNo. K-1313D), entitled “ROTATABLE CUTTING BIT ASEMBLY WITH WEDGE LOCKRETENTION ASSEMBLY.”

FIELD OF THE INVENTION

[0002] This invention relates to a roof bit assembly. More particularly,this invention relates to a roof bit insert assembly for securelyconnecting an insert onto a bit body.

BACKGROUND OF THE INVENTION

[0003] Roof bits are used in a violent environment in which heavy loadsand torques are continually applied to the roof bits at a high rate. Oneinch diameter roof bits are commonly operated at about 250-600 rpm and1000-8000 pounds thrust. These conditions also generate excessive heatat the tip end of the roof bit assembly.

[0004] A hard wear resistant insert for use in a center vacuum rotarydrill bit is typically formed of cemented tungsten carbide and issecured by brazing the insert within a slot formed within a top workingsurface of the body of the rotary drill bit. The hard wear resistantinsert secured within the top working surface of the rotary drill bitbody typically wears or dulls before the drill bit body becomes worn andunusable such that the user of the center vacuum rotary drill bit musteither replace the entire rotary drill bit, attempt to replace theinsert with a new insert of similar size, or attempt to resharpen theinsert. Replacement of the entire center vacuum rotary drill bit iscostly and resharpening of the insert may only be performed a limitednumber of times before the top working surface of the drill bit bodyfrictionally engages the material to be cut.

[0005] In U.S. Pat. Nos. 5,310,015; 5,184,925 and 5,226,489, to Woods etal., a roof bit assembly is disclosed wherein a support bar ispositioned between the insert bit and bit body for adjusting the heightthat the insert bit extends beyond the top surface of the roof bit body.In U.S. Pat. No. 5,184,925, the insert body has a semicircular notch 50therein and the support bar has a corresponding convex portion forcooperating with the depression. The support bar in these roof bitsresults in additional assembly time during original manufacturing orwhen replacing inserts onto a bit body. The assembly of these roof bitscan be even more time consuming and cumbersome in the field. The supportbar also requires maintaining additional parts and undesirable expandinginventories.

[0006] In U.S. Pat. No. 4,356,873, to Dziak, an insert is provided witha notch that cooperates with a projection 38 on a retainer clip thatmust be fixed into a slot of the bit body. The retainer clip islaterally held in position in the bit body slot by flanges 40 thatcooperate with the exterior cylindrical wall of the bit body.

[0007] There is a need in the industry for a mining roof bit thatrequires a minimum number of parts, is easy to assemble accurately,braze, and comparatively inexpensive in cost. There is also a need inthe industry for an insert that is securely held in the bit body duringdrilling operations and is not as readily knocked loose from the bitbody.

SUMMARY OF THE INVENTION

[0008] Briefly, according to this invention there is provided a centervacuum rotary drill bit including a rotary drill bit body and an insert.The rotary drill bit body includes a top working surface having a slotextending transversely across the top working surface. The slot includesa first sidewall, an opposite second sidewall and a bottom surfaceextending between the first sidewall and the second sidewall. The insertincludes a pair of oppositely facing generally parallel side surfaces, apair of oppositely facing end surfaces extending between andinterconnecting the side surfaces, a pair of oppositely inclined topsurfaces extending between and interconnecting the side and endsurfaces, and a bottom surface extending transversely to andinterconnecting the side and end surfaces. The bottom surface of theslot has a projecting key that cooperates with a depression keyway ofthe insert.

[0009] In one embodiment, generally vertical sidewall surfaces of adepression keyway and vertical sidewall surfaces of a projection keyprovide mechanical resistance against lateral movement of the cuttinginsert. This mechanical resistance reduces displacement of the insertwith respect to the bit body during brazing and thus a high quality,accurately aligned drill bit assembly is provided by applicants'invention. Additionally, it is believed that during drilling operationsthe vertical surfaces assist in resisting lateral displacement caused bylateral force loads and torques applied to the cutting ends of theinsert.

[0010] The depression keyway is designed so as to minimize the effect ofthe axial load on the insert by avoiding sharp corners which tend toamplify nominal stress and provides for an insert of a proper carbidedensity after pressing.

[0011] Integral bit body protuberance means contact the insert along theslot, the protuberance means are cylindrical ridges, semispherical,circular, prisms, angular or an equivalent shape or form. Theprotuberance means adequately separate the insert within the slot andpermit braze flow between the insert and slot. The protuberance meansenhance braze flow when braze is fed between the insert body and bitbody.

[0012] The overall bottom surface area of the cemented tungsten carbideinsert is significantly increased by the keyway depression. The key andkeyway increase the surface contact area between the bottom surface areaof the insert and cooperating bottom surface of the slot. The increasedsurface contact area allows for additional braze to be applied betweenthe insert and bit body slot enhancing the strength of the bond betweenthe insert and bit body.

[0013] Another added benefit of the depression keyway is that thedepression keyway in the tungsten carbide reduces the amount of tungstencarbide or other material needed to manufacture the insert. Incomparison to an insert bit dimensionally equivalent in shape and sizeto applicants' insert without a keyway, 30%-50% by weight less tungstenis needed to make applicant's insert bit. Cemented tungsten carbide isrelatively expensive and applicants, insert design significantly reducesmaterial costs.

[0014] The invention requires a minimum number parts for assembly,reduces material cost and provides for a strong and precisely assembledroof bit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further features and other aspects and advantages of thisinvention will become clear from the following detailed description madewith reference to the drawings in which:

[0016]FIG. 1 is a perspective view of a center vacuum rotary drill bitincluding an insert and bit body in accordance with the presentinvention;

[0017]FIG. 2 is a side view of FIG. 1 with a partial cross-section;

[0018]FIG. 2A is an enlarged side view and cross-section of the slot ofFIG. 2;

[0019]FIG. 3 is a top view of the roof bit shown in FIG. 1;

[0020]FIG. 4 is a side view of the insert bit used in FIG. 1;

[0021]FIG. 5 is a partial cross-sectional side view of a secondembodiment;

[0022]FIG. 6 is a perspective view of the bit body of the secondembodiment illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] In the following description, like reference characters designatelike or corresponding parts. Referring now to FIG. 1, there is shown acenter vacuum rotary drill bit assembly 10 including an elongatedcylindrical bit body 12 having a generally cylindrical section 26 and atop working surface 14.

[0024] The bit body 12 includes at least a pair of opposing dustcollection openings 18 angularly positioned with respect to a centralvertical axis 20 of the drill bit body. The dust collection openings 18are disposed within recessed surfaces 22. As shown in FIG. 1, theopenings 18 and recessed surfaces 22 cooperatively provide a pair ofoppositely disposed, generally transverse, arcuate shaped shoulderportions 24.

[0025] The top working surface 14 of the drill bit body 12 has anirregular surface configuration defined by an alternating first pair ofoppositely disposed trailing surfaces 28 and a second pair of oppositelydisposed tapered compression surfaces 30. The trailing surfaces 28 aregenerally parallel to the top surface of the insert and extenddownwardly and outwardly in a direction away from the vertical centralaxis 20 of the drill bit body 12 and provide a backup or support for aninsert 32. The tapered compression surfaces 30 are of a generallysemicircular shape. The lower edge of each of the compression surfaces30 abuts with the recessed surface 22, which together cooperatively actas a conduit for dust and the like to flow to the openings 18.

[0026] As shown in FIGS. 1-4, the drill bit body defines a transverselyextending slot 34 to receive an insert 32. The slot 34 includes a firstsidewall 36 and an opposite second sidewall 38 joined at the bottom edgethereof by slot bottom surface comprising two bottom surface sections 40connected by a generally central projection key 51. Preferably, thesidewalls 36 and 38 of the slot 34 are parallel to the vertical centralaxis 20 of the drill bit body 12. The generally centrally positionedinverted U-shape projection 51 functions as a key and support member.The bit body is cast from steel. Suitable steels for manufacturing thebit body would be either 4140 and 15B35 A.I.S.I (American Iron & SteelInstitute). Other suitable steel compositions are disclosed in U.S. Pat.Nos. 5,008,073 and 4,886,710, both to Greenfield.

[0027] The insert 32 secured within the slot 34 may be of a type havinga plate-like configuration and made of a high strength, wear-resistantmaterial such as cemented tungsten carbide and the like. The insert istypically made from a hard material such a tungsten carbide-cobaltalloy. Exemplary materials for the hard inserts include cobalt cementedtungsten carbide grades such as a Grade 1 that contains 5.4 weightpercent cobalt (the balance tungsten carbide), a tungsten carbide grainsize of 1-18 (micrometers), and a Rockwell A hardness of 88.2; a Grade 2that contains 6.3 weight percent cobalt with the balance being tungstencarbide; a tungsten grain size of 1-12 micrometers, and a Rockwell Ahardness of 89.6; and a Grade 3 that contains 6.0 weight percent cobalt(the balance being tungsten carbide), a tungsten carbide grain size of1-9 micrometers, and a Rockwell A hardness equal to 90.7. While theabove three grades are acceptable grades of cemented tungsten carbide,the preferred grade of cemented tungsten carbide for the hard inserts is***Kennametal Grade K3012E***.

[0028] As shown in FIG. 4, the insert 32 is an “A” frame house styletungsten carbide insert having a pair of oppositely facing, generallyparallel side surfaces 42 and a pair of oppositely facing end surfaces44. A pair of adjacent oppositely inclined top surfaces 46 extendbetween and interconnect the side 42 and end 44 pairs of surfaces andbottom surfaces 48 separated by an inverted U-shaped depression 50 thatfunctions as a keyway for receiving the U-shaped projection key 51. Theinsert bottom surfaces 48 are generally rectangular shape and are sizedrelative to the bit body slot 34 to fit within the slot in closelyspaced relation to the corresponding inner side walls 36 and 38 andbottom surfaces 40 of the slot.

[0029] The keyway 50 in the tungsten carbide reduces the amount oftungsten carbide or other hard material needed to manufacture theinsert. For instance, in comparison to an insert bit dimensionallyequivalent in size to applicants' insert that does not have a keyway orany other notches thereinbetween, 30-50% by weight less tungsten isneeded to make applicants' insert bit. Cemented tungsten carbide issignificantly more expensive per pound than the cost of steel used toconstruct the additional bit body key 51 that is needed to providesupport within the inverted U-shaped arch.

[0030] The U-shaped depression does not include any sharp edges and hasa smooth contour allowing for more uniform compaction duringmanufacturing. In pressing cemented tungsten carbide drill bit inserts,sharp edges of irregular, angular rough dyes result in nonuniformcompaction and density of the cemented tungsten carbide material. Thenonuniform density of cemented tungsten carbide results in materialweakness adjacent the sharp angular surfaces that is more susceptible tofracture. The bottom surfaces 48 adjacent the U-shape depression arerounded at the corners 41 to also insure more uniform carbide density atthe corners. The corners 41 have a radius of between 0.03-0.18 inches.Similarly, the apex of the bit insert where the two top inclinedsurfaces 46 meet can also be rounded for the same purpose.

[0031] Another benefit of having a U-shaped keyway 50 and projection key51 is that the generally vertical sidewall surface sections 53 of thekeyway and vertical surface sections 55 of the projection key providemechanical resistance against radially outward movement of the cuttinginsert. This mechanical resistance reduces dislocation of the insertwith respect to the bit body during assembly prior to brazing, duringbrazing and it is believed during operational use of the roof bit. Theheight of the vertical surface 53 is of sufficient height to ensure thatwhen the insert is positioned in the slot more than just a minimalamount of axial displacement must occur before the contacting verticalsurfaces of the insert 53 and projection key 55 are axially displaced soas to disengage. The height of the vertical surface 53 of the keyextends generally between 0.04-0.10 inches. When assembling the insertand bit body together the cooperating key and keyway enable the insertto be quickly and accurately positioned without the necessity ofmanually measuring and aligning the insert into its proper position onthe bit body. The cooperating key and keyway also substantially helpinterlock the insert to the bit body reducing the likelihood ofseparation failure in the field. Copending U.S. patent application Ser.No. 09/376,725, filed Aug. 17, 1999, to Ted R. Massa et al. (Case No.K-1313D), entitled “ROTATABLE CUTTING BIT ASEMBLY WITH WEDGE LOCKRETENTION ASSEMBLY” is herein incorporated by reference. Additionally,the contact surface area is significantly increased between thecooperating projection and depression surfaces which provides the addedbenefit of increased surface area for applying braze and improving thebond between the insert and bit body. Hence, the cooperating projectionkey and keyway depression enhance the connection between the insert andbit body by improving both physical resistance and the braze joint.

[0032] It is believed that an inverted U-shape concave depression 50better distributes an applied axial force during cutting or drilling bythe bit 10 thereby preventing fracture of the insert 32. It will beappreciated that the design of the concave U-shaped depression 50similar to a semicircular depression minimizes the effect of the axialload on the insert 32 during use by eliminating sharp corners thatamplify nominal stress.

[0033] As shown in FIGS. 1-4, the concave depression 50 is an invertedU-shape having a central axis perpendicular to the parallel sidesurfaces 42 of the insert. In another embodiment, the central axis ofthe concave depression 50 may be positioned at an oblique angle withrespect to the parallel side surfaces 42 of the insert.

[0034] As illustrated in FIG. 2A, the bit body slot has protuberancemeans shaped as integral ridges 57 along the bottom surface sections 40,on the top of the key 51 and on both sidewall surfaces 36 and 38 of theslot. The ridges 57 are for the intended purpose of providing gaps forbraze material to flow and penetrate between and around the insert andslot. The braze can be wire fed between the insert body and bit body. Asuitable braze alloy is HANDY HI-TEMP 548 braze alloy, manufactured andsold by Handy & Harmon, Inc., 859 Third Avenue, New York, N.Y. 10022.HANDY HI-TEMP 548 braze alloy is composed of 55+/−1.0 weight percentcopper, 6+/−0.5 weight percent nickel, 4+/−0.5 weight percent manganese,0.5+/−0.05 weight percent silicon, and the balance zinc with 0.50 weightpercent maximum on total impurities. Additional information on HANDYHI-TEMP 548 braze alloy may be found in Handy & Harmon Technical DataSheet D-74, available from Handy & Harmon, Inc.

[0035] Alternatively, the insert can be brazed to the bit body byemploying a braze material shaped to correspond to the shape of theinsert including a keyway. The braze material and insert are positionedinto the bit body slot and heated together in combination to melt thebraze that bonds the insert to the bit body.

[0036] The large U-shaped key central to the insert bit improves heattransfer away from the tip end of the bit body during drilling incomparison to prior art roof bits without a key and cooperating keyway.The bit body steel has a higher heat transfer conduction rate than thehard material (e.g., tungsten carbide) of the insert bit. Hence, onaccount of lower operating temperatures, it is believed that lowertemperature braze alloys than HANDY HI-TEMP 548 can be used. A lowertemperature brazing operation helps reduce the energy costs inmanufacturing the roof bit assembly.

[0037] In a second embodiment illustrated in FIGS. 5-6, in addition tothe protuberance along the bottom surface sections 40, on top of the key51 and on both sidewall surfaces 36 and 38 as in the first embodiment,protuberance means are positioned on the vertical surface sections 55 ofthe projection key 51. The protuberance means on these vertical sections51 allow for additional braze to flow into and fill a resulting gapbetween the insert and bit body

[0038] In other embodiments, the protuberance means that contact theinsert along the slot can be semispherical, circular, prisms or othershapes that adequately separate the insert within the slot and permitbraze flow between and about the insert and slot.

[0039] In FIG. 4, the width W and height H of the concave depression 50corresponds to the bit body key 51 shape and size, the height H andwidth W of the depression keyway can be varied in accordance with thehardness of the insert material, the hardness of the material beingdrilled and the overall width/height of the insert. For example, aninsert of approximately 1 inch diameter may have a keyway width ofapproximately 0.60 inches and height H of approximately 0.310 incheswith the overall height of the insert from bottom to peak of the topsurface being approximately 0.50 inches. On the other hand an inserthaving an overall width of approximately 1½ inch diameter may have adepression keyway width of approximately 0.90 inches. The height H andwidth W dimensions for the keyway depression and slot projection key aredesigned not to significantly compromise the performance, strength,fracture resistance and useful life of the insert in relation to priorart inserts of similar dimensions without a keyway.

[0040] Although the invention was primarily developed in connection witha center vacuum rotary drill bit, and is thus described with respectthereto, it will be readily apparent that applicants' improved insertspacer assembly may be used with equal facility for other tools such asrotary drill bits and the like. Accordingly, the description of theinvention in relation to a center vacuum rotary drill bit is not to beconstrued as a limitation on the scope of the invention.

[0041] The documents, patents and patent applications referred to hereinare hereby incorporated by reference.

[0042] Having described presently preferred embodiments of theinvention, it is to be understood that it may be otherwise embodiedwithin the scope of the appended claims.

What is claimed is:
 1. A rotary drill bit assembly comprising: a rotarydrill bit body having a top working surface and a slot extendingtransversely across said top working surface, said slot including afirst sidewall, an opposite second sidewall and a first bottom surfaceextending between said first sidewall and said second sidewall; aninsert positioned within said slot, said insert including a secondbottom surface having a U-shaped depression formed therein, said firstbottom surface having a U-shaped projection such that said projectionsupports said depression.
 2. The rotary drill bit assembly according toclaim 1 wherein a vertical surface portion of said U-shaped projectionprovides mechanical resistance to displacement of said insert from saidslot.
 3. The rotary drill bit assembly according to claim 1 wherein theU-shaped depression forms a void that makes said insert approximatelybetween 30%-50% by weight less than an insert of equal dimension withouta depression therein.
 4. The rotary drill bit assembly according toclaim 1 wherein said slot has a plurality of protuberance means forenhancing brazing.
 5. The rotary drill bit assembly according to claim 4wherein said U-shaped projection in said slot has said protuberancemeans for enhancing brazing.
 6. The rotary drill bit assembly accordingto claim 4 wherein said first and second sidewalls have protuberancemeans for enhancing brazing.
 7. The rotary drill bit assembly accordingto claim 4 wherein said U-shaped depression is smooth and does notinclude any sharp corners.
 8. The rotary drill bit assembly according toclaim 4 wherein the insert is connected to said bit body by brazing. 10.A bit body comprising: a slot wherein said slot includes a U-shapedprojection.
 11. The bit body according to claim 10 further comprising: acylindrical section; and a top working surface.
 12. The bit bodyaccording to claim 11 wherein said top working surface includes a pairof trailing surfaces and compression surfaces.
 13. The bit bodyaccording to claim 10 wherein said U-shaped projection has a pluralityof protuberance means for enhancing brazing.
 14. The bit body accordingto claim 13 wherein the protuberance means are ridges.
 15. The bit bodyof claim 10 wherein said bit body includes a generally cylindricalsection having dust collection openings therein.
 16. A bit bodycomprising: a slot having a plurality of protuberances for enhancingbrazing.
 17. A bit insert comprising: a pair of oppositely facinggenerally parallel side surfaces, a pair of oppositely inclined topsurfaces extending between said side surfaces and a U-shaped depressionextending upward from the bottom of said insert.
 18. The bit insertaccording to claim 17 wherein the U-shaped depression forms a void thatmakes said insert approximately between 30%-50% by weight less than aninsert of equal dimension without a depression therein.
 19. The bitinsert according to claim 17 wherein said U-shaped depression is smoothand does not include any sharp corners.
 20. The bit insert according toclaim 17 wherein a vertical surface portion of said U-shaped depressionprovides mechanical resistance to displacement from a bit body.
 21. Thebit insert according to claim 20 wherein said vertical surface portionis generally between 0.05-0.10 inches in height.
 22. A bit body forreceiving a bit insert comprising a slot having a bottom surface with anonlinear irregular shape whereby said bottom surface overall surfacecontact area is increased for the application of braze.
 23. A bit bodyaccording to claim 22 wherein said bottom surface includes protuberancemeans.
 24. A bit insert for attachment to a bit body comprising a bottomsurface having a nonlinear irregular shape whereby said bottom surfaceoverall surface contact area is increased for the application of braze.